Add a virtual _checkRole(bytes32) internal function to AccessControl (#3137)

* add a virtual _onlyRole(bytes32) modifier

* _onlyRole(role) → _checkRole(role)

* update doc

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+ * `AccessControl`: add a virtual `_checkRole(bytes32)` function that can be overriden to alter the the `onlyRole` modifier behavior. ([#3137](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3137))
+
 ## Unreleased
 
  * `ERC2981`: add implementation of the royalty standard, and the respective extensions for `ERC721` and `ERC1155`. ([#3012](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3012))

contracts/access/AccessControl.sol

@@ -67,7 +67,7 @@ abstract contract AccessControl is Context, IAccessControl, ERC165 {
      * _Available since v4.1._
      */
     modifier onlyRole(bytes32 role) {
-        _checkRole(role, _msgSender());
+        _checkRole(role);
         _;
     }
 
@@ -85,6 +85,18 @@ abstract contract AccessControl is Context, IAccessControl, ERC165 {
         return _roles[role].members[account];
     }
 
+    /**
+     * @dev Revert with a standard message if `_msgSender()` is missing `role`.
+     * Overriding this function changes the behavior of the {onlyRole} modifier.
+     *
+     * Format of the revert message is described in {_checkRole}.
+     *
+     * _Available since v4.6._
+     */
+    function _checkRole(bytes32 role) internal view virtual {
+        _checkRole(role, _msgSender());
+    }
+
     /**
      * @dev Revert with a standard message if `account` is missing `role`.
      *